Separation of oils and pitch from tar



R. LESSING. SEPARATION OF OILS AND PITCH FROM TAR. APPUCATION HLED SEPT. 9.19m.

1,405,234, Patented Jan. 31, 1922.

INVENTOR I are er BUIDOLF LESSING, OF LONDON, ENGLAND.

@EPATION' OF OILS AND FITCH FROM TAR.

Specification of Letters Patent.

Application filed September 9, 1918. serial No. 253,129.

To all whom it may concern:

Be it known that I, RUDOLF LnssING, a subject of the King of Great Britain, residing at London,England, have invented certain newand useful Improvements in the Separation of Oils and Pitch from Tar, of which the following is a specification.

The separation, on a manufacturing scale, of coal tar into oils and pitch has hitherto been effected mainly by distillation.

My investigations have led me to the con- I clusion that coal tar and like tars are considerably altered in composition during the process of distillation, whereln the temperature must be raised fairly high slnce the boiling points of the oils range up to 350.

6., and higher if production of hard pitch is an object, and the temperature of the mass in the retort is considerably in excess of this.

I have, therefore, sought to separate oils and pitch from coal tar or other mlxture thereof by a process having no effect on the composition of the constituents of the tar, or an effect less than that of the heat applied in the ordinary distillation, in the hope that more liquid oils and a more valuable pltch would be obtained than are produced by distillation.

According to my invention such a result is obtained by treating coal tar (preferably free from benzol, toluol, and solvent naphtha) with certain solvents, more particularly of a non-aromatic constitution and especially petroleum distillates consisting mainly of hydrocarbons of the paraffin 'or naphthene series. When a petroleum spirit, for instance, is mixed with coal tar the portion which is insoluble in the spirit constitutes a more or less hard pitch, and the portion which disv solves is left, after the petroleum spirit has been removed by distillation in the form of an oil, normally of red colour, liquid at ordinary temperature and of low viscosity, containing very little crystalline solid matter, such as naphthalene or anthracene; it is miscible readily with petroleum oils of any kind.

Coal tar can be thus separated into pitch and oils in proportions which maybe varied, at the ordinary temperature, but I prefer to operate at a temperature at which the whole mass remains sufiiciently liquid to permit thorough intermixture with the solvent. For this reason I prefer to use a solvent the bulk of which boils at a temperature above the melting point of the pitch produced in the process.

Forexample, the tar, having been dehydrated to free it from water and the benzol and naphtha fractions, is agitated or stirred with petroleum spirit at a temperature slightly below the boiling point of the latter. The mixture separates into a lower layer of pitch sufficiently liquid to be run off from the vessel and-an upper layer of a solution of oil in the spirit, which solution may be distilled for recovery of the spirit and isolation of the oil.

To use the solvent in a continuous cycle,

the coal tar may be charged into a vessel having a stirrer, suitable heating devices and a pipe for delivering solvent into the lower part of the charge from a reflux condenser. An overflow from the vessel permits the solution containing the oil to pass to a still the vapour from which is delivered to the said reflux condenser, whence the condensed vapour flows back into the charge of tar as aforesaid.

By withdrawing pitch continuously from the bottom of the vessel and oil from the still while permitting tar to flow at a corresponding rate into the vessel, continuity of Patented Jan. 31, 1922.,

process can be attained. When, on the other hand, the process is conducted intermittently, the progress of the saturation of each sequent increase of power consumed in stirring, I

The invention will be best illustrated by describing an actual operation and the apparatus in which it is performed Tar from which the bulk of the ammoniacal liquor, benzol, and naptha, have been removed enters the closed vessel A, (see the accompanying diagram) through pipe 1. It may be pre-heated or taken hot from a dehydration plant. Vessel A is fitted with stirring gear a or any suitablemeans for bringing the tar andsolvent into intimate contact. The tar sinks to the bottom opcupying from one-third to two-thirds of the vessel. The solvent, for instance a petroleum spirit substantially free from aromatic hydrocarbons and having a boiling range from 100 to 120, and a specific gravity of about 0.74, is. introduced into A through pipe 2, which enters the vessel at 3, and is provided with perforations for the effective distribution of the solvent. This rises through the tar or the partially-extracted pitch forming an oil solution which completely occupies the remainder of the vessel and overflows through pipe 4 into still B. In the drawing this is shown in the form of a column heated by closed steam which enters through pipes 12 and leaves through pipes 13. The column may be packed with any suitable tower filling oifering a large surface, or may be an ordinary column still.

The solution, which for satisfactory working should preferably contain not more than 40 per cent, of oil, trickles down the still and is gradually deprived of the solvent which rises in vapour form and leaves the still through pipe 5. The oily residue, free fromsolvent, is drawn off through outletcock 6, and may be passed through an oil cooler or heat inter-changer before being put into storage. Pipe 5 carrying the vapour enters a junction vessel C, provided with a sight glass, through which it is led into the cooling coil 7 of condenser D, the

cooling coil being open to the atmosphere.

' The vapours are condensed in this coil, the

condensate running through G into pipe 2, through which it is again delivered to vessel A. The same quantity of solvent 1s, therefore, circulated many times through the tar or the partially-extracted pitch in practically automatic fashion. The temperature in A is kept just below the boiling point of the solvent, say about 100 0., which suflices to keep the pitch fluid enough for easy agitation. The temperature can be regulated by the temperature of the inflowing tar'andsteam coils 9. In order to keep pipe 2 clear of pitch a plunger 10 is provided by means of which any fluid pitch may be forced through the perforations.

' As soon as the bottom layer of pitch is sufficiently free from oil it can be run off through cock 1 1.

The process may be carried out qulte con. tinuously, that is to say, a continuous stream of tar may enter through 1, and continuous streams of pitch and oil may leave the plant through 11 and 6 respectively, in

which case each zone in the lower part of A is kept in the same state of more or less complete extraction. The process may be carried out intermittently by charging 1ndividual batches of tar into A, extract1ng the tar progressively, and runnmg ofi'. the pitch when the desired degree of extract on is attained. Likewise the distillation of splrit maybe carried out intermittently by keeping all the oily residue in st1ll 'B- (1n th1s case of the pot-still type) and runn ng it off when the batch is completed,

Any combination of these modes of working can be employed. For instance, it may- 2 for the removal water from the condensate. It is understood that the plant described in the drawing is only one form in which my process may be carried out.

When it is an object to remove phenols and other acid constituents from the tar oils, the solution produced by my process may be washed with a' suitable alkaline liquid. A convenient mode of doing this is tO 'lIlterpose between the vessel A and the still B, a closed vessel supplied intermittently or continuously with caustic soda solution through which solution the solution contained in A is caused to flow on its way to the still in the same manner in which the solvent flows through the tar in vessel A. The caustic soda solution may-she run off from the interposed vessel continuously or intermittently correspondingly with the manner in which it is fed to the vessel. If pyridine or other tar bases are to be re moved, a like procedure may be followed with substitution of an acid liquid for the alkaline liquid.

Having now particularly described an ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is 1. The process of treating tar containing light aromatic hydrocarbons to obtain ure tar oils free of bitumen, and pitch, w ich consists in removing the light aromatic hydrocarbons from the tar, introducing the tar into a vessel, maintaining the temperature of the vessel at a heat sufiicient to kee the resulting pitch in a fluid state, intro ucing into said vessel a solvent of the tar oils only,said solvent being derived from petroleum and having a boiling point above the temperature within the vessel and lower than the boiling point of the tar oils, removing the resulting solution from the resulting itch, and raising the temperature of said so lution above the boiling point of the solvent and below the boiling point of the oils to recover the solvent and oils separate lly. 4

2. he process of treating tar containing aromatic hydrocarbons to obtain pure tar oils free of bitumen, and pitch, which consists in removing the light aromatic hydrocarbons from the tar, heating the tar and maintaining it at a temperature sufiiciently high to kee the resultin pitch in afluid state, intro ucing into said heated tar petroleum spirit to, dissolve the tar oils only and raising the temperature of said solution above the boiling point of the solvent and below the boiling point of the oils to recover the solvent and oils separately.

3. The process of treating tar containing lightaromatic hydrocarbons to obtain pure tar oils ,free of bitumen, and pitch, which consists in removing the light aromatic hydrocarbons, introducing the tar from which the light aromatic hydrocarbons have been removed continuously into a vessel, the temperature of which is sufficient to keep the resulting'pitch in a fluid state, introducing continuously into said vessel a solvent of the tar oils only, said solvent being derived from petroleum and having a boiling point above the temperature within the vessel and lower than the boiling point of the tar oils, continuously removing the resulting solution and raising the temperature of said solution above the boiling point of the solvent and below the boiling point of the oils, recovering the resulting oils and the solvent separately, returning the solvent to the vessel,

and withdrawing the resulting pitch from the vessel.

4. The process of treating tar containing light aromatic hydrocarbons to obtain pure tar oils free of bitumen, and pitch, which consists in removing the light aromatic hydrocarbons, introducing the tar from which the light aromatic hydrocarbons have been removed continuously into a vessel, the temperature of which is suflicient to keep the resulting pitch in a fluid state, introducing continuously into said vessel a solvent of the tar oils only, said solvent being derived from petroleum and having a boiling point above the temperature within the vessel and lower than the boiling point of the tar oils, continuously removing the resulting solution and raisin the temperature of said solution above t e boiling point of the solvent and below the boiling point of the oils,

recovering the resulting oils and the solvent separately, returning the solvent to the vessel, and intermittently withdrawing the resulting pitch from the vessel.

In testimony whereof I afiix my signature in presence of two witnesses.

RUDOLF LESSING. [L. s.] Witnesses:

T. J. OSMAN, B. H. DERHAM. 

